Driveline Vibration On Hard Acceleration

[88C1500]

A little past history on my 88 C1500 w/TH400

Transmission was removed and taken to a transmission rebuilder because of an issue with the Transmission Front Pump making noise.

Previous to the rebuild I did not notice any driveline vibrations.

After getting the trans returned and re-installed, the Front Pump noise was eliminated, but extreme vibrations could be felt in the trans or driveline, on moderate to hard acceleration. Since working with the rebuilder was about as useless as catching fish in a dry lake, I've decided to fix this condition on my own. Here's the brand new parts I've replaced with little to no benefit in reducing the imbalance.

Transmission flex plate

Transmission Torque Converter

Motor Mounts

Motor Vibration Damper

Driveshaft Univeral Joints.

 

My suspicion is a thrust bearing or something not re-inserted in the tranny (snap ring?). Any ideas? or if I go with a replacement transmission, who would you recommend?